Technical Field
The present invention relates to a power conversion apparatus that includes a switch circuit, a feedback section and a signal generating section.
Related Art
In burst mode operation based on conventional art, switching frequencies that fall in an audible frequency band may cause audible noise. Therefore, a technique has been developed, aiming to avoid such frequencies that cause audible noise. For example, an invention dealing with such a technique is disclosed in patent document JP-B-4765081, entitled “Method and apparatus for reducing audible frequency in a switching power supply”. According to the technique, control is exerted over periods corresponding to groups of switching cycles of a switch, and over non-switching periods corresponding to intervals between the groups of switching cycles of the switch.
Further, it is desirable that high efficiency is achieved at low cost over an entire range from a light load period to a heavy load period. For example, patent document JP-A-2003-324953 discloses an invention dealing with a technique for achieving high efficiency at low cost, entitled “Switching power supply apparatus”. The control means in this invention stops the intermittent turn-on/off operation of the switching element when the first voltage detecting means has detected the increase of a first output voltage up to a first threshold. Further, the control means in this invention starts the intermittent turn-on/off operation of the switching element when a second voltage detecting means has detected the decrease of the first output voltage down to a second threshold.
However, despite the application of the invention disclosed in the patent document JP-B-4765081 to an apparatus, a response lag may be caused in the feedback control in the event that load current has drastically decreased, such as when an output connector has been disconnected. The response lag may lead to too much increase of the output voltage. Therefore, the output side is required to be provided with parts that can withstand high voltage (high-voltage parts), which would necessarily incur high cost.
Further, despite the application of the invention disclosed in the patent document JP-A-2003-324953 to an apparatus, the operation of the switching element is controlled on the basis of the first output voltage and the two thresholds (first and second thresholds). This may raise a problem that the average output voltage value varies between the two thresholds. Resultantly, there may be a range in which the average output voltage value is deviated from an instructed output voltage value and accordingly the output voltage cannot be controlled with high accuracy.